Field-induced diffusion of gold and related phase transformations in the C60 and C70 fullerenes

The intercalation of metal M (M = Au, Ag, In) from the electrode into the polycrystalline C-60 and C-70 thin films is studied by time-dependent and space-resolved conductivity measurements under controlled oxygen-free atmosphere at different temperatures and electric fields. The time resistivity behavior is interpreted on the basis of electric-field-induced diffusion of metal ions from the electrodes to the interstitials of the fullerene crystal lattice and local formation of MxC60 and MxC70 phases. A comparison between the resistivity behaviors of C-60 and C-70 thin films provides evidence that the process is sensitive to the electronic level structure of the fullerenes molecules. [S0163-1829(99)08823-2].